There are mainly three methods- electric resistance welding, electro-slag welding and induction pressure welding. In electric resistance welding, which is a nonfusion welding process, heat is generated by the passage of current across the interface of the joint. This method is extensively used in spot and seam welding where sheet metals are pressed together at the joint by copper alloy electrodes. Quality and finish depends upon current, pressure, pressure duration, current duration, work piece material and thickness of work piece. Spot and seam welding are the common electric resistance welding processes. Some other types of electric resistance welding are projection welding, upset butt welding and flash butt welding. Spot welding is used in aircraft industries, auto and instrument industries. Spot welding is common since it doesn’t require skilled man power. Process is very fast and we can achieve mass production with very clean welding. Seam welding is preferred for steels, aluminium, magnesium and nickel alloys. Projection welding is used in heavy steel stampings, in the encapsulation of thyristers and in welding brackets. Upset butt welding is used for joining tubes. Flash butt welding is used in solid and tubular structural assembly, gears and rings, boilers etc.
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